Resin sheets having glass fiber reinforcements are well known in the construction trades and such sheets are used particularly as liners in refrigerator compartments and in the transportation industry have been used as liners for railway cars and trucks.
Such sheets have been made by passing a glass fiber mat through a bath of thermosetting resin, encasing the glass fiber mat with resin contained therein between top and bottom films and passing this structure between spaced rolls to squeeze out surplus resin and to gauge the thickness of the resulting sheet, after which the sheet is heated to set the resin. One such manufacture is set forth in Menzer U.S. Pat. No. 2,980,574; another is set forth in my U.S. Pat. No. 3,480,497 and still another is set forth in Menzer U.S. Pat. No. 3,137,601. Another is set forth in the Finger U.S. Pat. No. 2,969,301.
Several difficulties have been encountered when practicing the prior methods. When a resin layer is laid down and a glass fiber layer put on top of it, and this combination placed between films and passed between rollers, the glass fibers next to the resin layer may get properly impregnated but the fibers on the other side of the glass layer are very likely not to be properly impregnated or may be irregularly impregnated, resulting in a poor quality product.
While it is possible to use a pre-formed mat of glass fibers and run the mat of fibers through a resin bath, the pre-forming of the mat adds to the cost of the product and in addition the dipped glass mat is sticky and cannot be easily handled by machinery.
The Menzer U.S. Pat. No. 3,137,601 (which is assigned to the same assignee as the present application) introduces the outer films in such a way as to form a V shaped pocket between them, and roving cutters sprinkle glass fibers onto the surface of the resin pool contained in this pocket. But a difficulty of this system is that the glass fibers tend to stay in a layer on the surface of the pool and it is difficult to get them to descend into the lower part of the pool in any kind of distributed fashion. This may be due to the fibers becoming interconnected at the surface or for some other reason, but in any event the difficulty persists.
I have discovered that by laying the thermosetting resin down on one of the cover films and placing a glass fiber layer over the resin and then passing this composite downwardly through a pool of resin and between the spaced rolls, it is possible to control the amount of resin with respect to the rate at which the glass fiber layer is passed between said rolls so that the pool is maintained, and in this way a sandwich structure can be prepared which, when subjected to heat, forms a reinforced sheet of the finest quality.